This invention relates to steam engines and particularly to steam engines in which steam at atmospheric to slightly above atmospheric pressure in the steam chamber of a cylinder is exposed to a vacuum causing a power stroke. In particular, this invention is directed to steam-to-vacuum engines having two cylinders having linked pistons, each cylinder of which has a steam chamber which may be exposed to steam at or slightly above atmospheric pressure, which steam exits the cylinder creating a vacuum in that cylinder which permits ambient air pressure to push one of the linked pistons through a power stroke.
The development of modern steam power began with the Savery pump patented by Thomas Savery in 1698, which was used to remove water from mines. It worked by heating water to vaporize it, filling a tank with steam, then creating a vacuum by cutting off the tank from the steam source and then injecting cold water into the tank to condense the steam. The resulting vacuum was used to draw water up from a mine.
Thomas Newcomen (1663–1729) improved on the Savery pump by combining a steam cylinder and piston with a pivoting beam. The beam is heavier on the side opposite the steam cylinder so that gravity pulls that side down. As the heavy side descends, the piston in the steam cylinder rises. Power is created by filling the cylinder with steam at about atmospheric pressure and then spraying water into the cylinder to condense the steam. The resulting vacuum allows atmospheric pressure to push the piston down causing the side of the beam above the cylinder to pivot down and further causing the heavy side of the beam to ascend, filling a pump below the ascending side with water. At the bottom of the power stroke, a valve opens to restore steam to the cylinder, allowing the heavy side of the beam to be pulled back down by gravity to activate the pump. Thus, the Newcomen engine was driven by atmospheric pressure pushing on a piston to fill a vacuum using steam at about atmospheric pressure. Newcomen's engines were inefficient primarily because the steam cylinder was repeatedly heated and cooled, wasting energy to heat the cylinder.
James Watt (1736–1819) made a pioneering breakthrough in 1765 with his discovery that a great efficiency could be achieved by using a separate condenser. Like Newcomen's atmospheric engine, Watt's engine also operates on the principle of atmospheric pressure pushing a piston down. However, valves permit the steam to be sucked into the separated condenser for cooling of the steam and creation of the vacuum. Separating the condenser allows the steam piston and cylinder to remain hot at all times resulting in a substantial increase in efficiency over Newcomen's engine.
Subsequent improvements to steam engine technology focused primarily on high pressure steam and new mechanical designs, leaving production of power using atmospheric pressure vacuum engines relegated to the sidelines.